1. Field of the Invention
The present invention relates to a pedal apparatus of an electronic musical instrument, the pedal apparatus having characteristics of reaction force similar to those of a pedal of an acoustic piano.
2. Description of the Related Art
As for an acoustic piano which is a natural musical instrument, particularly, a grand piano, when a player of the acoustic piano depresses a damper pedal, the player recognizes the gradient of reaction force imposed by the damper pedal. That is, the player recognizes that the rate of change in reaction force (increment value of reaction force divided by increment value of the amount of stroke) varies according to the depth of depression of the damper pedal (stroke). FIG. 5 indicates an overview of characteristics of reaction force of a lever (a damper pedal or a shift pedal) of a grand piano. The vertical axis indicates the load applied to the lever, while the horizontal axis indicates the amount of displacement (the amount of stroke) of the lever. A characteristic curve 61 indicates the amount of stroke of the damper pedal to which the load is applied. The load is perceived by the player as a reaction force when the player depresses the damper pedal.
The damper pedal is connected to dampers through some connecting portions. In an initial state where the player starts depressing the damper pedal, respective weights of the dampers and the connecting portions contribute to production of an initial reaction force, resulting in a great rate of change in reaction force. Then, while the amount of stroke of the damper pedal is small, the force exerted by the player to depress the damper pedal will not be conveyed to the dampers because of interstices of the connecting portions. While the amount of stroke of the damper pedal falls within a shown area A0, therefore, the rate of change in reaction force is small except the initial state. If the player increases the amount of stroke of the damper pedal further, the amount of stroke enters a shown area A1 where the force exerted by the player in order to depress the damper pedal is conveyed to the dampers through the connecting portions to start lifting the dampers which are in contact with strings. Because of elastic elements which the respective connecting portions have and increased friction produced by uneven moves of the neighboring dampers, in the area A1, the rate of change in reaction force increases. When the amount of displacement of the damper pedal increases further to enter an area A2, all the dampers fully leave the strings to stop the increase in the reaction force caused by the elastic elements which the respective connecting portions have. In the area A2, as a result, the rate of change in reaction force of the damper pedal decreases again. When the amount of stroke then enters an area A3, the damper pedal comes into contact with a stopper, resulting in a sharp increase in the rate of change in reaction force.
A shown area AH (an area ranging from the latter half of the area A1 to the neighborhood of the boundary between the areas A1, A2) is generally referred to as a half pedal area. Advanced players subtly change the amount of depression of the damper pedal in the half pedal area AH to change the timbre, reverberation and the like of musical tones to be generated. By recognizing varying rates of change in reaction force in the boundary between the area A1 and the area A2, the advanced players realizes that the amount of stroke of the damper pedal is in the half pedal area. Depending on the types and manufacturers of grand pianos, respective structures of the damper pedal, the connecting portions and the dampers vary. Therefore, respective start positions and respective widths of the shown areas A0, A1, AH, A2 vary among grand pianos. Some grand pianos have characteristics, as indicated by a characteristic line 62 indicated by a dashed line, that there is no difference in the rate of change in reaction force between the areas A0, A1.
The grand piano also has a shift pedal. In response to the player's depression of the shift pedal, a mechanism for striking the strings moves in the direction in which keys of a keyboard are arranged. As a result, one of two or three strings provided for each key will not be struck by a hammer. The shift pedal exhibits characteristics of reaction force similar to those of the above-described damper pedal indicated by the characteristic curve 61. In the area A0, however, the shift pedal exhibits the characteristics indicated in the figure by the characteristic curve 62 of the dashed line. The characteristic curve 61 indicates the characteristics exhibited when the damper pedal is depressed. A characteristic curve exhibited when the damper pedal is released indicates that the reaction force of the released damper pedal is slightly smaller than that of the depressed damper pedal with respect to the same amount of displacement of the damper pedal. The difference in the reaction force between the depressed damper pedal and the released damper pedal is caused by hysteresis produced by viscosity and friction forces of the connecting portions. The shift pedal exhibits a larger hysteresis than the damper pedal.
In general, conventional pedal apparatuses of electronic musical instruments are designed such that a damper pedal is urged by one spring. As a result, the gradient of reaction force does not change. However, there is a known art applied to a pedal apparatus of an electronic musical instrument in order to vary the rate of change in reaction force exerted by a damper pedal according to the amount of stroke of the damper pedal (Japanese Unexamined Patent Publication No. 2004-334008). The disclosed art employs two spring members so that the spring members can act on a damper pedal step by step. The art exhibits characteristics in which the reaction force starts increasing at some point during the stroke of the damper pedal. However, the characteristics exhibited by the disclosed art provide the player with a sense of touch which is different from that offered by the damper pedal of the grand piano indicated in FIG. 5. In addition, the damper pedal of the conventional art requires the player to apply a greater force in order to fully depress the damper pedal than that required when the player fully depresses the damper pedal of the grand piano.